During the ageing of metal oxide NPs a crystallization of MexOy moities performed and number of structural defects related to non-controlled cluster aggregation reduced. This is resulted in appearance of required properties (depend on type of metal oxide selected). Non-aged NP do not have appropriate properties. Substantial deviation from ageing conditions leads to aggregation of NPs to bulk oxide and also loosening of valuable characteristics. And finally this behaviour is typical for many other compounds.